Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02536767 2005-11-O1
FY.S 1064CA0 PATENT
VALVE TRAIN DEVICE FOR ENGINE
BACKGROUND OF THE INVENTION
Field of the Invention
(0001] This invention relates to a valve train device for an engine, and more
particularly to a valve train device which can continuously change valve
opening duration
and the amount of valve lift.
Description of the Related Art
[0002] For example, a valve train device for an engine capable of continuously
changing intake valve opening duration and the amount of valve lift has been
practically
used. This type of valve train device is constituted to cause a camshaft to
drive an intake
valve to open and close through a rocker arm, in a way such that a swing
member driven to
swing by the camshaft is provided, and a control arm is interposed between a
swing cam
surface of the swing member and a rocker-side depressed surface of the rocker
arm.
Changing a position of the control arm to come into contact with the swing cam
surface and a
position of the control arm to come into contact with the rocker-side
depressed surface causes
the valve opening duration and the amount of valve lift to continuously vary
(See JP-A-Sho
59-500002, for example).
SUMMARY OF THE INVENTION
[0003] Using the aforementioned constitution, in which the position of the
control
arm to come into contact with the rocker-side depressed surface is changed, in
the
conventional type of valve train device may result in a problem, depending on
where the
rocker-side depressed surface is disposed, with lovV transfer efficiency of
force, applied from
the swing cam surface to the control arm, and transferred to the rocker arm
and therefore to
the valve.
[0004] This invention is made in view of the situations with the prior art
described above. An object of the invention is to provide a valve train device
for an engine
which can enhance transfer efficiency of the force, applied to the control
arm, and transferred
to the rocker arm and therefore to the valve.
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[0005] The invention of Claim 1 is a valve train device 7 for an engine
adapted to
swing a rocker arm 11 swingably supported on a rocker shaft 14 to drive a
valve 3 which
opens and closes a valve opening 2b formed in a combustion chamber 2a, the
device 7
including: a swing member 9 swingably disposed and driven by drive means 8; a
control arm
10, which is disposed between a swing cam surface 9b formed on the swing
member 9 and a
rocker-side depressed surface 1 1d formed on the rocker arm 11, for
transferring motion of the
swing cam surface 9b to the rocker-side depressed surface lid; and a
displacement mechanism
for displacing contact points of the control arm 10 with the swing cam surface
9b and with
the rocker-side depressed surface 11 d, in which the rocker-side depressed
surface lid is
formed in an arcuate shape about a center of swing (a) of the swing member 9,
such that the
rocker-side depressed surface 11 d or its extension line 11 d' passes in the
vicinity of a center
of swing (b) of the rocker arm 11.
[0006] In the invention, the description "such that the rocker-side depressed
surface lid or its extension line l 1d' passes in the vicinity of a center of
swing (b) of the
rocker arm 11" means that the rocker-side depressed surface l 1d is
approximated as close as
possible to a straight line Lo that connects the center of swing (b) and a
point (f) of
application of force F transferred from the control arm 10 to the rocker arm
11, thereby
transferring the force F with high efficiency as the rotational force of the
rocker arm 11.
[0007] The invention of Claim 2 is the valve train device 7 for an engine
according to Claim 1, in which the rocker arm 11 includes: left and right
rocker arm portions
11 a supported by the rocker shaft 14; and a rocker coupling portion lib for
coupling the left
and right rocker arm portions l la into one, and the control arm 10 has: a
control arm portion
10a that forms a control-side depressing surface l Ob to come into contact
with the rocker-side
depressed surface l 1d on the rocker arm portion side at the distal end of the
control arm; and
a roller l Oc as recited in Claim 3 or a contact portion provided at the
distal end of the control
arm portion 10a to come into contact with the swing cam surface 9b, the
control arm being
placed to be interposed between the left and right rocker arm portions 11a,
and the rocker-
side depressed surface 1 1d being formed on the rocker coupling portion l 1b.
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[0008] The invention of Claim 3 is the valve train device 7 for an engine
according to Claim 2, in which the contact portion is a roller supported with
the distal end of
the control arm portion.
[0009] The invention of Claim 4 is the valve train device 7 for an engine
according to Claim 1, in which the rocker arm 21 has a rocker arm portion 21b
supported
with a rocker shaft 24, the control arm 20 includes a roller 20c which comes
into contact with
the swing cam surface 9b, the roller 20c is positioned externally to the
rocker arm portion
21b, and a roller shaft 20b for supporting the roller 20c has a control-side
depressing surface
which comes into contact with the rocker-side depressed surface 21 d formed on
the rocker
arm 21.
[0010] The invention of Claim 5 is the valve train device 7 for an engine
according to any one of Claims 2 through 4, in which the displacement
mechanism is
constituted such that an eccentric pin 14b is provided on a midsection of the
rocker shaft 14,
a proximal end l Of of the control arm portion 10a is rotatably coupled with
the eccentric pin
14b, and rotating the rocker shaft 14 allows displacing the contact point
between the roller
lOc and the swing cam surface 9b and the contact point between the control-
side depressing
surface lob on the control arm portion 1 Oa and the rocker-side depressed
surface 11 d.
[0011] The invention of Claim 6 is the valve train device 7 for an engine
according to Claim 5, in which the rocker-side depressed surface 11 d or its
extension line lid'
passes inside a rotation locus C of an axial center (c) of the eccentric pin
14b, which is
generated by rotating the rocker shaft 14.
(0012] The invention of Claim 7 is the valve train device 7 for an engine
according to Claim 5 or 6, in which offset displacement of the eccentric pin
14b is preset
such that an outer surface 14b' thereof protrudes outward from an outer
surface 14a' of the
rocker shaft 14 in the radial direction, and an inner peripheral surface of
the bearing portion
11 c of the rocker arm 11 supported on the rocker shaft 14 is formed with a
clearance recess
11 f which conforms with the amount of protrusion of the eccentric pin 14b.
[0013] The invention of Claim 8 is the valve train device 7 for an engine
according to any one of Claims 5 through 7, in which the displacement
mechanism is
constituted such that displacement of the contact point relative to the
rotation angle of the
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rocker shaft 14 in a low or high operation range, in which the opening
duration of the valve 3
is short or long and the amount of the valve lift is. small or large, is
smaller than the
displacement of the contact point in a medium operation range in which the
opening duration
of the valve and the amount of the valve lift are medium.
[0014] The invention of Claim 9 is the valve train device 7 for an engine
according to any one of Claims 5 through 8, in which a coupling portion of the
control arm
portion 10a with the eccentric pin 14b includes: a semi-circular-shaped
bearing portion lOd
formed at and integrally with the proximal end of the control arm portion 10a,
and rotatably
supported with the eccentric pin 14b; and a come-off prevention member 15 for
preventing
the bearing portion l Od and the eccentric pin 14b from separating from each
other.
[0015] The invention of Claim 10 is the valve train device 7 for an engine
according to Claim 9, in which the come-off prevention member 15 is a leaf
spring for
holding the bearing portion l Od of the control arm portion 10a and the
eccentric pin 14b, and
the leaf spring has a depressing portion 15b integrally formed therewith and
urging the
control arm 10 by depressing the rocker arm 11 such that the roller lOc comes
into contact
with the swing cam surface 9b.
(0016] The invention of Claim 11 is the valve train device 7 for an engine
according to any one of Claims 5 through 10, in which the control arm 10 is
brought into
sliding contact with a step 14c from the eccentric pin 14b of the rocker shaft
14, thereby
being positioned in the axial direction, and the rocker arm 11 is brought into
sliding contact
with the axial end surface lOf of the control arm 10, thereby being positioned
in the axial
direction.
[0017] The invention of Claim 12 is the valve train device 7 for an engine
according to any one of Claims 1 through 11, in which the center of swing (a)
of the swing
member 9 is located at a point opposite to a shaft line L1 of the valve 3 with
respect to a
straight line L2 parallel to the shaft line L 1 of the valve and passing the
axial center (b) of the
rocker shaft 14.
[0018] According to the invention of Claim 1, as shown in FIG. 3, the control
arm
is designed to transfer the motion of the swing cam surface 9b of the swing
member 9 to
the rocker-side depressed surface lid of the rocker arm 11. In this case, the
rocker-side
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depressed surface 11 d is formed in an arcuate shape about the center of swing
(a) of the
swing member 9, such that the rocker-side depressed surface 11 d or its
extension line lid'
passes in the vicinity of the center of swing (b) of the rocker arm 11. Thus,
the force F
applied from the swing member 9 to the control arm 10 can be efficiently
transferred to the
rocker arm 11 and therefore to the valve 3.
[0019] To be more specific, the force F transmitted from the control arm 10 to
the
rocker arm 11 is divided into a first component force (rotational force of the
rocker arm) F1
perpendicular to the direction of a straight line Lo that connects a point (f)
of application of
the force F and the center of swing (b) of the rocker arm, and into a second
component force
F2 in the direction of the straight line Lo. In the invention, since the
rocker-side depressed
surface 11 d or its extension line lid' passes in the vicinity of the center
of swing (b) of the
rocker arm 11, the rocker-side depressed surface l 1d generally agrees with
the straight line
Lo. This decreases the second component force F2 while increasing the first
component
force Fl, which results in enhanced transfer efficiency of the force F from
the control arm 10
to the rocker arm 11.
[0020] According to the invention of Claims 2 and 3, the control arm 10 is
placed
to be interposed between the left and right rocker arm portions 11 a, 11 a of
the rocker arm 11,
and the rocker-side depressed surface 11 d is formed on the rocker coupling
portion 11 b for
coupling the left and right rocker arm portions 11 a, 11 a. This enables the
rocker-side
depressed surface 11 d or its extension line 11 d' to be formed to pass in the
vicinity of the
center of swing (b) of the rocker arm 11, thereby achieving enhanced
transmission efficiency
of the force from the control arm 10 to the rocker arm 11.
(0021] According to the invention of Claim 4, the control arm 20 is provided
with
the roller 20c which comes into contact with the swing cam surface 9b such
that the roller is
located externally to the rocker arm portion 21b of the rocker arm 21, and the
roller shaft 20b
for supporting the roller 20c is designed to depress the rocker-side depressed
surface 21d of
the rocker arm portion 21 b. This enables the rocker-side depressed surface 21
d or its
extension line 21 d' to be formed to pass in the vicinity of the center of
swing (b) of the rocker
arm 21, thereby achieving enhanced transfer efficiency of the force from the
control arm 20
to the rocker arm 21.
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[0022] According to the invention of Claim 5, the proximal end of the control
arm
portion 1.0a is rotatably coupled with the eccentric pin 14b provided on the
midsection of the
rocker shaft 14, and rotating the rocker shaft 14 allows displacing the
contact point between
the roller lOc and the swing cam surface 9b and the contact point between the
control-side
depressing surface 1 Ob and the rocker-side depressed surface 11 d. This
allows the opening
duration of the valve 3 and the amount of the valve lift to continuously
change by using a
very simple structure, that is, solely rotating the rocker shaft 14.
[0023] According to the invention of Claim 6, the rocker-side depressed
surface
11 d or its extension line 11 d' passes inside the rotation locus C of the
axial center (c) of the
eccentric pin 14b, which is generated by rotating the rocker shaft 14. Thus,
enhanced
transmission efficiency of the force from the control arm 10 to the rocker arm
11 can be more
certainly achieved.
[0024] According to the invention of Claim 7, offset displacement of the
eccentric
pin 14b is so preset that the outer surface 14b' of the eccentric pin 14b
protrudes outward
from the outer surface 14a' of the rocker shaft 14 in the radial direction.
This can increase
the displacement of the control arm 11 without increasing the diameter of the
rocker shaft 14,
thereby increasing the adjustment range for the valve opening duration and
amount of the
valve lift.
[0025] For the eccentric pin 14b protruding outward, an inner peripheral
surface
of the bearing portion 1 lc of the rocker arm 1 l, which is supported on the
rocker shaft 14, is
formed with the clearance recess 11 f which conforms with the amount of
protrusion of the
eccentric pin 14b. Thus, while the clearance recess 11 f fits the protrusion
of the eccentric pin
14b, the rocker arm 11 is displaced in the axial direction of the rocker shaft
14, so that the
rocker arm 11 can be assembled to the rocker shaft 14 without any problem.
[0026] According to the invention of Claim 8, the displacement of the contact
point relative to the rotation angle of the rocker shaft 14 in a low operation
range, in which
the opening duration of the valve 3 is short and the amount of the valve lift
is small, is preset
smaller than the displacement of the contact point in a medium operation range
in which the
opening duration of the valve 3 and the amount of the valve lift are medium.
This, in the low
engine speed range, can avoid abrupt variations in engine output due to slight
variations in
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rotation angle of the rocker shaft 14, and can provide smooth operations,
thereby avoiding
jerky feeling.
[0027] The displacement of the contact point in a high operation range, in
which
the opening duration of the valve 3 is long and so forth, is preset smaller
than the
displacement of the contact point in a medium operation range. This, in the
high engine
speed range, can reduce a torque required for rotating rocker shaft 14, and
can provide
smooth driving operations.
(0028] According to the invention of Claim 9, the semi-circular-shaped bearing
portion lOd is formed at and integrally with the proximal end of the control
arm portion a,
and rotatably supported with the eccentric pin 14b, and the come-off
prevention member is
provided for preventing the bearing portion lOd and the eccentric pin 14b from
separating
from each other. This facilitates work for coupling the control arm 10 and the
eccentric pin
14b.
[0029] To be more specific, in the case of multi-cylinder engine, adjustments
for
uniform valve opening duration and amount of the valve lift are needed for all
cylinders.
Therefore, several control arms 10 within the dimensional tolerance range are
prepared for
selecting a combination to uniform the valve opening duration and the amount
of the valve
lift. Assembly and removal of the control arm to be carried out for selecting
the combination
are required to be easy. The invention can meet such a requirement.
[0030] According to the invention of Claim 10, the come-off prevention member
is a leaf spring 15 for holding the bearing portion l Od of the control arm
portion 10a and the
eccentric pin 14b. This further facilitates the assembly/removal of the
control arm 10 to/from
therockershaft 14.
(0031] Also, the leaf spring 15 has the depressing portion 15b integrally
formed
therewith and urging the control arm 10 by depressing the rocker arm 11 such
that the roller
lOc comes into contact with the swing cam surface 9b. Thus, the roller lOc of
the control
arm 10 can be constantly in contact with the swing cam surface 9b of the swing
member 9
with a simple constitution. Therefore, a rolling contact of the roller lOc
with respect to the
motion of the swing cam surface 9b can be kept normal, thereby preventing the
wearing of
the swing cam surface 9b and the roller l Oc.
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[0032] According to the invention of Claim 11, the control arm 10 is brought
into
sliding contact with the step 14c from the eccentric pin 14b of the rocker
shaft 14, thereby
being positioned in the axial direction. Also, the rocker arm 11 is brought
into sliding
contact with the axial end surface lOf of the control arm 10, thereby being
positioned in the
axial direction. Therefore, positioning of the control arm 10 and the rocker
arm 11 in the
axial direction can be achieved without any dedicate parts.
[0033] According to the invention of Claim 12, the center of swing (a) of the
swing member 9 is located at a point opposite to the valve shaft line L1 with
respect to the
straight line L2 parallel to the valve shaft line L1 and passing the axial
center (b) of the
rocker shaft 14. This gives advantage to the rocker-side depressed surface lld
or its
extension line 11 d' to pass in the vicinity of the center of rotation (b) of
the rocker arm 11.
More specifically, as an angle formed between the direction of the force F
applied to the
rocker arm 11 and the straight line Lo that connects the point (f) of
application of the force F
and the center of swing (b) of the rocker arm 11 is closer to the right angle,
the transfer
efficiency of the force increases. Since the center of swing (a) of the swing
member 9 is
located on the side opposite to the valve shaft line L1, the direction of the
force F can be
easily set perpendicular to the direction of the straight line Lo.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a sectional side view of a valve train device for an engine
according to a first embodiment of the present invention.
[0035] FIG. 2 is a perspective view of a control arm, rocker arm and rocker
shaft
of the first embodiment.
[0036] FIG. 3 is a sectional side view for describing functions and effects of
the
invention.
[0037] FIG. 4 is a schematic view showing one of variations of a come-off
prevention member of the first embodiment.
[0038] FIG. 5 is a sectional side view for describing a second embodiment of
the
invention.
[0039] FIG. 6 is a schematic top plan view of the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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[0040] An embodiment of the present invention will be described hereinafter
with
reference to the attached drawings.
[0041] Figs. 1 to 3 are intended to describe an first embodiment of the
invention.
FIG. 1 is a sectional side view of a valve train device according to the
embodiment of the
invention. FIG. 2 is a perspective view of core parts of the valve train
device. FIG. 3 is a
view for describing transfer efficiency of a force F in the invention.
[0042] In FIG. 1, reference numeral 1 denotes a valve device for opening and
closing valve openings formed in a combustion chamber. The valve device 1 has
the
following constitution. In this embodiment, only a portion at an intake valve
side is shown.
An engine is provided with two intake and exhaust valves. A combustion recess
2a is
provided on the mating face of a cylinder head 2 of the engine with the
cylinder body. The
combustion recess 2a forms a top ceiling of a combustion chamber. The
combustion recess
2a includes left and right intake valve openings 2b. Each intake valve opening
2b is merged
with an intake port 2c and led to an external connection opening of an engine
wall. Each
intake valve opening 2b is opened and closed through a valve head 3a of an
intake valve 3.
The intake valve 3 is constantly urged with a valve spring (not shown) in
closing direction.
[0043] A valve train device 7 is disposed above the intake valve 3. The valve
train device 7 is constituted such that: an intake camshaft 8 which serves as
swing member
driving means causes a swing member 9 to swing, the swing member 9 causes a
rocker arm
11 to swing through a control arm 10, and the swing of the rocker arm 11
causes the intake
valve 3 to proceed and retract in the axial direction, and thus the intake
valve opening 2b is
opened and closed.
[0044] Causing the control arm 10 to proceed and retract can continuously
change
a contact point between the control arm 10 and the swing member 9 and a
contact point
between the control arm 10 and the rocker arm 11, thereby continuously
changing the
opening duration of the intake valve 3 and the amount of valve lift.
[0045] The intake camshaft 8 is arranged in parallel with a crankshaft (not
shown)
and supported to be rotatable and immobile in the direction perpendicular to
the intake
camshaft and in the axial direction through a cam journal portion formed on
the cylinder head
2 and a cam cap provided on an upper mating face of the journal portion. The
intake
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camshaft 8 is formed with a single cam nose 8c common to the left and right
intake valves,
including a base circle portion 8a having a specified diameter, and a lift
portion 8b having a
specified cam profile. Each cylinder is provided with a single cam nose.
[0046] The swing member 9 has a pair of left and right swing arm portions 9a,
9a,
a swing cam surface 9b, a roller shaft 9c, and a swing roller 9d. The pair of
swing arm
portions 9a, 9a is supported for free swinging movement by a swing shaft 12
arranged in
parallel with the intake camshaft 8 immobilized in the direction perpendicular
to the swing
shaft and in the axial direction. The swing cam surface 9b is formed to
connect the front
ends (lower ends) of the swing arm portions 9a. The roller shaft 9c is
arranged in parallel
with the swing shaft 12 and in the midsection between the left and right swing
arm portions
9a, 9a to pass therethrough. The swing roller 9d is rotatably supported on the
roller shaft 9c.
The swing roller 9d is constantly in rotational contact with the cam nose 8c.
[0047] Base portions (upper ends) of the swing arm portions 9a is fitted to
and
supported with the swing shaft 12 for free swinging movement. The swing shaft
12 is
provided with a pair of left and right balance springs 13 as coil springs.
Each balance spring
13 has an end 13a retained between the swing shaft 12 of the swing arm portion
9a and the
roller shaft 9c, and the other end 13b of each balance spring is retained by
the cylinder head
2. The balance spring 13 urges the swing member 9 such that the swing roller
9d of the
swing member 9 comes into contact with the cam nose 8c of the intake camshaft
8, thereby
preventing the swing roller 9d from moving away from the cam nose 8c at the
high engine
speed. This avoids abnormal behavior of the swing member 9.
[0048] The swing cam surface 9b has a base circle portion 9e and a lift
portion 9f
formed together in a curved manner to have a connected surface and has
generally a plate-like
shape. The swing member 9 is provided so that the base circle portion 9e is
positioned nearer
to a rocker shaft 14 and the lift portion 9f is positioned opposite the rocker
shaft 14. The base
circle portion 9e has an arcuate shape of a radius R1 centered on the axis of
the swing shaft
12 as the center of swing (a). Thus, while the base circle portion 9e
depresses the roller l Oc,
the intake valve 3 is placed at a fully closed position and not lifted even if
a swing angle of
the swing member 9 increases.
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[0049] Meanwhile, the lift portion 9f lifts the intake valve 3 greatly as the
lift
portion 8b of the intake camshaft 8 at the portion close to the top depresses
the swing roller
9d, that is, as the swing angle of the swing member 9 increases. In this
embodiment, the lift
portion 9f includes a ramp zone which gives a constant speed, an acceleration
zone which
gives a varied speed, and a lift zone which gives generally a constant speed.
[0050] The rocker shaft 14 includes a large-diameter portion 14a and an
eccentric
pin 14b having a smaller diameter than the one for the large-diameter portion.
The eccentric
pin 14b is provided on a midsection of the large-diameter portion, while being
offset from an
axial center (b) of the rocker shaft 14 toward the outer side in the radial
direction. The large-
diameter portion 14a is rotatably supported with the cylinder head 2. The
eccentric pin 14b
has an axial center (c) positioned such that part of the outer surface 14b'
protrudes outward in
the radial direction from an outer surface 14a' of the larger-diameter portion
14a. To the
rocker shaft 14 is connected a rocker shaft driving mechanism (not shown) for
controlling an
angular position of the rocker shaft 14 according to an engine load (throttle
opening) and
engine speed.
(0051] The rocker arm 11 is formed with left and right rocker arm portions l
la,
11 a, a rocker coupling portion 11 b, and ring-shaped bearing portions 11 c,
11 c. Lower-half
portions on the distal end side of the left and right rocker arm portions 11
a, 11 a are coupled
integrally with the locker coupling portion 11b. The ring-shaped bearing
portions l lc, l lc
are formed integrally with the proximal ends of the left and right rocker arms
11 a, 11 a. The
bearing portions 11 c, 11 c are supported with the large-diameter portions
14a, 14a of the
rocker shaft 14. Part of the bearing portions llc towards the rocker arm
portions lla is
provided with a clearance recess l if that conforms to the outwardly
projecting shape of the
eccentric pin 14b.
[0052] The control arm 10 has a schematic structure in which: a control-side
depressing surface lOb is formed in an arcuate shape about the center of swing
(a) on the
lower face of the distal ends of the left and right bifurcated control arm
portions 10a, a; the
roller lOc in rotational contact with the swing cam surface 9b is pivoted
between the distal
ends of the control arm portions a, a; and the bifurcated, semi-circular
bearing portion lOd is
formed at the proximal ends of the control arm portions.
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[0053] On the topside of the rocker coupling portion l 1b of the rocker arm
11,
left and right rocker-side depressed surfaces 11 d, 11 d are formed to come
into sliding contact
with the left and right control-side depressing surfaces 10b, 10b. The rocker-
side depressed
surfaces 11 d, 11 d are formed in an arcuate shape of a radius R2 about the
center of swing (a)
of the swing shaft 12. An extension line 11 d' of the rocker-side depressed
surface 11 d is so
set as to pass in the vicinity of the center of swing (b) of the rocker arm
11, and more
specifically, to pass inside a rotation locus C of the axial center (c) of the
eccentric pin 14b.
[0054] The control arm 10 is placed such that it is interposed between the
left and
right rocker arm portions 11 a, 11 a of the rocker arm 11. The semi-circular
bearing portion
lOd is rotatably supported with the eccentric pin 14b of the rocker shaft 14.
The come-off
prevention spring 15 prevents the bearing portion and the eccentric pin from
coming off.
[0055] The come-off prevention spring 1 S is made of spring steel band member,
and has a holding portion 15a curved into approximately a C-shape and a
depressing portion
15b that extends from the front end of the holding portion 15a toward the
distal end of the
rocker arm 11 . The come-off prevention spring 1 S is designed to retain a
curved retaining
portion 15c, which is formed adjacent to the boarder between the holding
portion lSa and the
depressing portion 15b, to a retained portion 10e of the control arm 10. The
come-off
prevention spring 1 S is also designed to retain an accurate retaining portion
15d, which is
formed opposite to the pressing portion 15b, to the eccentric pin 14b.
Thereby, the come-off
prevention spring 15 holds the bearing portion lOd and the eccentric pin 14b
together for
relative rotation while preventing them from separating from each other.
[0056] The distal end of the depressing portion 15b of the come-off prevention
spring 15 comes into contact with a depressing groove 11 a with a
predetermined amount of
spring force, the depressing grove being provided on the topside of the rocker
coupling
portion 11 b of the rocker arm 11 and at the center in the axial direction.
The depressing
groove 11 a is formed in an arcuate shape about the center of rotation (a) of
the swing member
9. In the manner as described, the control arm 10 is urged clockwise as shown
in the
drawing. The roller l Oc comes into contact with the swing cam surface 9b. A
slight gap (d)
is created between the rocker-side depressed surface 11 d and the control-side
depressing
surface 10b.
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[0057] In the manner as described, a displacement mechanism is constituted
such
that rotating the rocker shaft 14 allows a contact point (e) between the
roller lOc and the
swing cam surface 9b as well as a contact point (f) between the control-side
depressing
surface 1 Ob and the rocker-side depressed surface 11 d to displace.
[0058] In the displacement mechanism, displacement of the contact point
relative
to the rotation angle of the rocker shaft 14 in a high operation range in
which the opening
duration of the intake valve 3 is long and the amount of the valve lift is
large (shown by solid
lines in FIG. 1) and in a low operation range in which the opening duration of
the intake
valve 3 is short and the amount of the valve lift is small (shown by chain
double-dashed lines
in FIG. 1) is smaller than the displacement of the contact point in a medium
operation range
in which the opening duration of the intake valve 3 and the amount of the
valve lift are
medium. In other words, in the high operation range, the axial center of the
eccentric pin 14b
is positioned near (c 1 ), while near (c2) in the low operation range. When
the eccentric pin
14b is adjacent to (c1) or (c2), each displacement of the contact point (e)
and (f) relative to
the rotation angle of the rocker shaft 14 is smaller than that in another
operation range. In
contrast, in the medium operation range, the axial center of the eccentric pin
14b is
positioned approximately between (c1) and (c2). When the eccentric pin 14b is
adjacent
approximately between (c1) and (c2), each displacement of the contact point
(e) and (f)
relative to the rotation angle of the rocker shaft 14 is larger than those in
the other operation
ranges.
[0059] An axial end surface lOf of the bearing portion lOd is in sliding
contact
with an end surface 14c of the large-diameter portion 14a of the rocker shaft
14, the end
surface forming a step from the eccentric pin 14b, thereby positioning the
control arm 10 in
the axial direction. In turn, an inner end surface 11 c'of the bearing portion
11 c is in sliding
contact with an opposite end surface to the end surface l Of of the bearing
portion lOd of the
control arm 10, thereby positioning the rocker arm 11 in the axial direction.
[0060] Description will be next made of the operations and effects of this
embodiment.
[0061] In the valve train device 7 of this embodiment, the rocker shaft
driving
mechanism controls a rotational angular position of the rocker shaft 14 in
accordance with
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CA 02536767 2005-11-O1
engine operation conditions determined based on the engine speed and load. For
example, in
a high-speed and high-load operation range, the angular position of the rocker
shaft 14 is
controlled to position the axial center of the eccentric pin 14 to (c1) as
shown by solid lines in
FIG. 1. Thus, when the control arm 10 is positioned at the advanced end and
the base circle
portion 8a of the camshaft 8 comes into contact with the roller 9d, the
contact point (e)
between the roller lOc of the control arm 10 and the swing cam surface 9b of
the swing
member 9 is positioned closest to the lift portion 9f . This results in
maximizing both the
opening duration of the intake valve 3 and the amount of valve lift.
[0062] In turn, in a low-speed and low-load operation range, the angular
position
of the rocker shaft 14 is controlled to position the axial center of the
eccentric pin 14 to (c2)
as shown by chain double-dashed lines in FIG. 1. Thus, the control arm 10
moves to the
retracted end, and the contact point (e) between the roller lOc of the control
arm 10 and the
swing cam surface 9b of the swing member 9 is positioned farthest from the
lift portion 9f.
This results in minimizing both the opening duration of the intake valve 3 and
the amount of
valve lift.
[0063] In this embodiment, the rocker-side depressed surface l 1d is formed
such
that the extension line 11 d' thereof passes in vicinity of the center (b) of
swing of the rocker
arm 11. More specifically, the following structure is used to allow the
extension line 11 d' to
pass inside the rotation locus C (see FIG. 3) of the eccentric pin 14. In
other words, the
control arm 10 is placed to be interposed between the left and right rocker
arm portions 11 a,
l la of the rocker arm 11, and the rocker-side depressed surface l 1d is
formed on the rocker
coupling portion 11 b for coupling the left and right rocker arm portions 11
a, 11 a. This
enables the extension line 11 d' of the rocker-side depressed surface 11 d to
pass in the vicinity
of the center (b) of swing of the rocker arm 11.
[0064] The rocker-side depressed surface l 1d is formed in such a manner that
the
extension line 1 1d' thereof passes in the vicinity of the center (b) of swing
of the rocker arm
11. Thus, the force F transferred from the swing member 9 to the contact point
(f) via the
control arm 10 can be efficiently transferred to the rocker arm 11 and
therefore to the valve 3.
In other words, in this embodiment, since the rocker-side depressed surface 11
d passes in the
vicinity of the center (b) of swing of the rocker arm 11, the rocker-side
depressed surface 11 d
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CA 02536767 2005-11-O1
generally agrees with the straight line Lo. This increases a first component
force F1 of the
force F, the first component force F 1 being perpendicular to the straight
line Lo as a
rotational force of the rocker arm 11, the force F being transferred from the
control arm 10 to
the rocker arm 11. Thus, the transfer efficiency of the force F from the
control arm 10 to the
rocker arm 11 enhances.
[0065] The center (a) of swing of the swing member 9 is located at a point
opposite to a valve shaft line L1 with respect to a straight line L2 parallel
to the valve shaft
line L1 and passing the axial center (b) of the rocker shaft 14, while being
away from the
straight line L2 by (g). This gives advantage to the extension line l 1d' of
the rocker-side
depressed surface 11 d to pass in the vicinity of the center (b) of rotation
of the rocker arm 11.
More specifically, as an angle formed between the direction of the force F
applied to the
rocker arm 11 and the straight line Lo that connects a point (f) of
application of the force F
and the center (b) of swing of the rocker arm 11 is closer to the right angle,
the transfer
efficiency of the force F increases. Since the center (a) of swing of the
swing member 9 is
located on the side opposite to the valve shaft line Ll, the direction of the
force F can be
easily changed to be close to the direction perpendicular to the straight line
Lo.
[0066] The eccentric pin 14b provided on the midsection of the rocker shaft 14
is
adapted to support the bearing portion l Od of the control arm portion a for
free rotation, and
the come-off prevention spring 15 holds the bearing portion lOd and the
eccentric pin 14b.
This allows the opening duration of the valve 3 and the amount of valve lift
to continuously
change by using a very simple structure or solely rotating the rocker shaft
14. This also
facilitates work for coupling the control arm 10 and the eccentric pin 14b.
[0067] In the case of multi-cylinder engine, because uniform valve opening
duration and amount of valve lift need be ensured for all cylinders, several
control arms 10
within the dimensional tolerance range are prepared to be selected in
combination with the
rocker shaft 14 in order to uniform the valve opening duration and the amount
of valve.
Assemble and removal work when such a selective combination is required can be
easily
carried out.
[0068] The depressing portion 15b is integrally formed with the come-off
prevention spring 15, the depressing portion 15b urging the control arm 10 by
depressing the
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CA 02536767 2005-11-O1
rocker arm 11, such that the roller lOc comes into contact with the swing cam
surface 9b.
Thus, the roller lOc of the control arm 10 can be constantly in contact with
the swing cam
surface 9b of the swing member 9 by a simple constitution. Also, a rolling
contact of the
roller l Oc with respect to the motion of the swing cam surface 9b can be kept
normal, thereby
preventing the wearing of the swing cam surface 9b and the roller l Oc.
[0069] Offset displacement of the eccentric pin 14b is so preset that the
outer
surface 14b' of the eccentric pin 14b protrudes outward from the outer surface
14a' of the
rocker shaft 14 in the radial direction. This can increase the displacement of
the control arm
11 without increasing the diameter of the rocker shaft 14, thereby increasing
the adjustment
range for the valve opening duration and amount of valve lift.
[0070] When the eccentric pin 14b protrudes outward, an inner peripheral
surface
of the bearing portion 11 c supported with the rocker shaft 14 of the rocker
arm 11 is formed
with the clearance recess 11 f which conforms with the amount of protrusion of
the eccentric
pin 14b. Thus, while the clearance recess 11 f of the rocker arm 11 fits the
protrusion of the
eccentric pin 14b, the rocker arm 11 is displaced in the axial direction of
the rocker shaft 14,
so that the rocker arm 11 can be assembled with the rocker shaft 14 without
any problem.
[0071] In the low operation range in which the opening duration of the valve 3
is
short and the amount of valve lift is small, the eccentric pin 14b is
positioned at (c2) so that
the displacement of the contact point (e) relative to the rotation angle of
the rocker shaft 14 is
smaller than the displacement in the medium operation range in which the
opening duration
of the valve 3 and the amount of valve lift are medium. This, in the low
engine speed range,
can avoid abrupt variations in engine output due to slight variations in
rotation angle of the
rocker shaft 14, and can provide smooth operations, thereby avoiding jerky
feeling.
[0072] In the high operation range in which the opening duration of the valve
3 is
long and so forth, the eccentric pin 14b is positioned at (c1) , so that the
displacement of the
contact point (e) relative to the opening angle of the rocker shaft 14 is
preset smaller than the
displacement in the medium operation range in which the opening duration of
the valve is
medium and so forth. This, in the high engine speed range, can reduce a torque
required for
rotating rocker shaft 14, and can provide smooth driving operations.
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CA 02536767 2005-11-O1
[0073] The control arm 10 is brought into sliding contact with the step 14c
from
the eccentric pin 14b of the rocker shaft 14, thereby positioning the control
arm in the axial
direction. The rocker arm 11 is brought into sliding contact with the axial
end surface l Of of
the control arm 10, thereby positioning the rocker arm in the axial direction.
Therefore,
positioning of the control arm 10 and the rocker arm 11 in the axial direction
can be achieved
without any dedicate parts.
[0074] In the description of the first embodiment, the come-off prevention
member is a leaf spring. However, as shown in FIG. 4, the come-off prevention
member of
the invention may be a rod-shaped come-off prevention pin whose both ends are
press-fitted
through the outer ends of the bearing portion 1 Od.
[0075] In the description of the first embodiment, the control arm is included
in
the rocker arm. However, the control arm may be disposed externally to the
rocker arm in the
invention.
[0076] Figs. 5 and 6 are for describing a second embodiment in which the
control
arm is disposed externally to the rocker arm. In the figures, the same
reference numerals as
in Figs. 1 to 4 designate the same or corresponding parts.
[0077] A rocker arm 21 includes: a cylindrical bearing portion 21 a supported
with
a large-diameter portion 24a of a rocker shaft 24; and left and right rocker
arm portions 21b,
21 b integrally extending forward from axially opposite ends of the bearing
portion 21 a.
Bottom surfaces of the distal ends of the rocker arm portions 21b come into
contact with the
top ends of left and right intake valves 3, 3, respectively.
[0078] Rocker-side depressed surfaces 21 d are formed on the topside of the
left
and right rocker arm portions 21b. The rocker-side depressed surfaces 21d are
formed in an
arcuate shape of a predetermined radius about an axial center of a swing shaft
12. An
extension line 21 d' of the rocker-side depressed surface 21 d is so set as to
pass in the vicinity
of a center of swing (b) of the rocker arm 21, and more specifically, to pass
inside a rotation
locus C of an axial center (c) of an eccentric pin 24b.
[0079] The control arm 20 includes a pair of left and right arm portions 20a,
20a,
a roller shaft 20b and proximal end portions 20d of the left and right arm
portions 20a, 20a.
The roller shaft 20b rigidly connects the distal ends of the left and right
arm portions 20a, 20a
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together. The proximal end portions 20d, which are formed in a semi-circular,
are coupled
and supported with the eccentric pin 24b of the rocker shaft 24, and retained
together with the
eccentric pin by the leaf spring, using the same constitution as in the first
embodiment.
[0080] The left and right arm portions 20a, 20a are positioned externally to
their
associated rocker arm portions 21 b, 21 b in the axial direction. Each arm
portion and the
associated rocker arm portion form a clearance between them to accommodate a
roller 20c.
The rollers 20c, 20c are supported with the roller shaft 20b for free
rotation. The rollers 20c
are in rotational contact with a swing cam surface 9b of the swing arm 9.
[0081] The roller shaft 20b is in sliding contact with the left and right
rocker-side
depressed surfaces 21 d, 21 d of the rocker arm 21. In other words, in this
embodiment, the
roller shaft 20b has a control-side depressing surface for depressing the
rocker-side depressed
surface 21 d.
[0082] The second embodiment of the invention is constituted in a way such
that:
the arm portions 20a of the control arm 20 are placed externally to the rocker
arm portions
21b of the rocker arm 21, the roller 20c is placed between the arm portion and
the rocker arm
portion, and the roller shaft 20b depresses the rocker-side depressed surface
21d. This
enables the rocker-side depressed surface 21 d to be formed such that an
extension line 21 d'
thereof passes in the vicinity of the center of swing (b) of the rocker arm
21. This can
enhance transfer efficiency of force from the control arm 20 to the rocker arm
21 as with the
case in the first embodiment.
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